Originally Posted by Kris Deering
I don't think that is how it works. He didn't build in a multiplier to everything. BUT, if you had put in that your max is 100 nits for low (which means your measured is about 50 nits) you are essentially building in a 2x multiplier already. Stacey built a 100 nit test pattern into the new 4K disc at my request. It is in the advanced video section. I believe it is one of the last patterns in the list. You could measure there and see.
The problem with setting a generic 2x for everything 100 nit and below is you are assuming that everyone did this with SDR, which isn't the case. Most of my clients want it brighter (most ask for around 20 fL, not 14-16). What Jim is doing is leaving as much range as he can nit for nit, but you have to build in for what will eventually be the curve. And that curve is going to be different depending on how high the content needs to stretch. So if you are putting in a higher display max light, you are getting more nit for nit range before the curve starts, but there isn't a hard fast rule that I'm aware of. I looked at the graphical representation of his curves when I was at his place a month or so ago and you could see the most of the curves were nit for nit for most of the same amount until you got to the really high nit values.
Thanks Kris, but I think you've misunderstood what I meant slightly - I'm wasn't suggesting a x2 low ratio should be baked in, I was just using it as an example to determine where we might be able to measure a pattern to verify results. We need something to adjust mid-tone brightness to taste (I run SDR at 18FtL also) - if the 'Low Ratio' setting is it, then fair enough.
Running though the example just for the sake of clarity:
- You measure a peakY off screen of 150nits
- So you set a 6x multiplier for DML giving 900
- And you set a low ratio to achieve a 2 x ratio of your measured peakY = 300 nits (which currently comes out around 28) [again the 2x multiplier is just an example, you could use x1.8 or x2.2 or whatever to taste]
By definition does that mean that the nit for nit range is output at 1/2 the luminance of the source (as you've used a 2x multiplier when setting the low ratio)?
Given those figures then, and assuming the above assumption on the nit-for-nit range is correct - is it then safe to deduce that 100 nits and below will definitely be within the nit-for-nit range?
If so, on that basis we should be able to throw up a 100nit HDR test pattern and measure 50 nits. If it doesn't, then we can adjust DML or Low Ratio until we hit 50nits. Of course our target can be higher or lower to taste; e.g. 40nits off the 100nit pattern, or 60 nits off the 100 nit pattern - but at least we have a system to verify the multiplier to the nit-for-nit range rather than eyeballing it alone.
What that also allows us to do is match the APL of the nit-for-nit range between two system - so if one user has a peakY of 150nits, and another has a peakY of 100nits, but they both adjust Low Ratio until they measure the same nits from a 100nit test pattern - the mid-tone luminance should be identical, and their images in the nit-for-nit range should be very similar (assuming similar accurate 2.4 gamma base calibrations).
I'll consider stumping up for the new Spears disc then, and try that pattern and see what happens.